1. Field of the Invention
The present invention relates to a method making novel organo functionalized silane precursors and polymers of the same that are applicable for thin films used for example as dielectrics in integrated circuits, optoelectronic applications and for other similar applications. In particular, the invention concerns first making an intermediate monomer and then converting the monomer to an organo functionalized silane monomer and finally forming a polymer or polymer compositions of the functionalized monomers. The invention also concerns a method for producing such films by preparing siloxane compositions by polymerization of the organo functionalized monomers, by applying the polymerized compositions on a substrate in the form of a layer and by curing the layer to form a film. Further, the invention concerns integrated circuit and optoelectronic devices and methods of manufacturing them.
2. Description of Related Art
The commercial use of electronic image sensors in electronics and, in particular in consumer electronics, has increased dramatically over the last few years. Electronic image sensors are found in cameras, cell phones, and are used for new safety features in automobiles e.g. for estimating distances between vehicles, protecting and detecting blind spots not exposed by mirrors etc. Many semiconductor manufacturers are converting production lines to CMOS sensor production to meet this demand. CMOS sensor manufacturing uses many of the processes currently used in standard IC manufacturing and does not require large capital investment to produce state of the art devices.
Processing from the bottom up a photodiode is built in the silicon layer. Standard dielectrics and metal circuitry are built above the diode to transfer the current. Directly above the diode is an optically transparent material to transfer light from the device surface and through a color filter to the active photo-diode. Transparent protection and planarization material is typically placed over the color filters and device. The micro-lenses are built over the planarized layer above the color filters in order to improve device performance. Finally a passivation layer maybe placed over the lens or alternatively a glass slide is placed over the lens array leaving an air gap between the lens and the cover. Most CMOS sensors are built using subtractive aluminum/CVD oxide metallization with one or more levels of metal. For the manufacturing of planarizing layer or micro-lenses are also used organic polymers such as polyimide or novolac materials or maybe sometimes siloxane polymers.
Organic polymers can be divided into two different groups with respect to the behavior of their dielectric constant. Non-polar polymers contain molecules with almost purely covalent bonds. Since they mainly consist of non-polar C—C bonds, the dielectric constant can be estimated using only density and chemical composition. Polar polymers do not have low loss, but rather contain atoms of different electronegativity, which give rise to an asymmetric charge distribution. Thus polar polymers have higher dielectric loss and a dielectric constant, which depends on the frequency and temperature at which they are evaluated. Several organic polymers have been developed for dielectric purposes. However, applicability of these films is limited because of their low thermal stability, softness, and incompatibility with traditional technological processes developed for SiO2 based dielectrics. For example, organic polymer cannot be chemical mechanical polished or etched back by dry processing without damaging the film.
Therefore some of recent focus has been on SSQ (silsesquioxane or siloxane) or silica based dielectric and optical materials. For SSQ based materials, silsesquioxane (siloxane) is the elementary unit. Silsesquioxanes, or T-resins, are organic-inorganic hybrid polymers with the empirical formula (R—SiO3/2)n. The most common representative of these materials comprise a ladder-type structure, and a cage structure containing eight silicon atoms placed at the vertices of a cube (T8 cube) on silicon can include hydrogen, alkyl, alkenyl, alkoxy, and aryl.
Many silsesquioxanes have reasonably good solubility in common organic solvents due to their organic substitution on Si. The organic substitutes provide low density and low dielectric constant matrix material. The lower dielectric constant of the matrix material is also attributed to a low polarizability of the Si—R bond in comparison with the Si—O bond in SiO2. The silsesquioxane based materials for microelectronic application are mainly hydrogen-silsesquioxane, HSQ, and methyl-silsesquioxane, (CH3—SiO3/2)n (MSQ). MSQ materials have a lower dielectric constant as compared to HSQ because of the larger size of the CH3 group ˜2.8 and 3.0-3.2, respectively and lower polarizability of the Si—CH3 bond as compared to Si—H. However, these films index of refraction at visible range typically around 1.4 to 1.5 and always less than 1.6.
The silica-based materials have the tetrahedral basic structure of SiO2. Silica has a molecular structure in which each Si atom is bonded to four oxygen atoms. Each silicon atom is at the center of a regular tetrahedron of oxygen atoms, i.e., it forms bridging crosslinks. All pure of silica have dense structures and high chemical and excellent thermal stability. For example, amorphous silica films, used in microelectronics, have a density of 2.1 to 2.2 g/cm3. However, their dielectric constant is also high ranging from 4.0 to 4.2 due to high frequency dispersion of the dielectric constant which is related to the high polarizability of the Si—O bonds. Therefore, it is necessary to replace one or more Si—O—Si bridging groups with C-containing organic groups, such as CH3 groups, which lowers the k-value. However, these organic units reduce the degrees of bridging crosslinks as well increases the free volume between the molecules due to steric hindrance. Therefore, their mechanic strength (Young's modulus <6 GPa) and chemical resistance is reduced compared to tetrahedral silicon dioxide. Also, these methyl-based silicate and SSQ (i.e., MSQ) polymers have relatively low cracking threshold, typically on the order of 1 μm or less.